Adolescents with alcohol related problems are increasingly being recognized as a heterogeneous population, with multiple developmental trajectories leading to alcohol use disorders. Psychologically traumatic experiences are among the environmental factors often postulated to contribute to the development of adolescent alcohol use disorders. In our current investigation, a substantially higher proportion of adolescents with alcohol use disorders than community controls have experienced trauma and posttraumatic stress disorder (PTSD). This study s designed to test the hypothesis that PTSD symptoms and abnormalities in biological stress response systems comprise the mechanisms through which trauma adversely influences the development and course of alcohol use disorders. This hypothesis will be tested through three integrated studies; (1) a cross- sectional stud utilizing a neuroendocrine laboratory assessment and structured equation modeling to examine the relationships among trauma, indices of catecholamine system and hypothalamic-pituitary-adrenal axis activities, pTSD symptoms, and alcohol related problems; (2) a prospective study determining the impact of trauma and PTSD symptoms on short-term and long-term outcome for adolescents with alcohol use disorders; and, (3) a prospective study examining whether or not trauma and PTSD symptoms predict alcohol-related problems in adolescents without alcohol use disorders at baseline. The results of this study will determine the mechanisms governing the impact of trauma on alcohol use disorders in adolescents, will identify specific areas important for relapse prevention and will lead to the development of specific methods for identifying adolescents at high risk for alcohol use disorders for preventative interventions.